Water-reducing agent
Water-reducing agent is also known as plasticizer or dispersant. Adding magnesium water-reducing agent when mixing concrete can make the concrete particles finer and more uniform, and at the same time drain out the water encapsulated in the concrete particles, thus significantly reducing the water demand of the concrete.
The function of the water-reducing agent is to improve the workability of the concrete without changing the mix proportion; or to improve the workability of the concrete without changing the workability. Reduce water demand and improve concrete rebound; or reduce concrete dosage while maintaining strength without changing, saving concrete and controlling costs. At the same time, the addition of water-reducing admixtures to concrete separates more evenly, improves a series of physical properties, such as waterproofing, cold resistance, adhesion resistance, etc., and improves the performance of concrete.
In the past, the water-reducing agents used in hydraulic concrete were usually general water-reducing agents such as paper pulp wastewater, calcium lignin, and molasses. The water-reducing rate was not high. Usually 5% to 10%. As the quality requirements for hydraulic concrete have improved, the quality requirements for water-reducing agents have also become higher and higher. Naphthalene-based high-efficiency water-reducing agents are widely used in large and medium-sized hydropower projects such as Ertan and Xilingxia. The water reduction rate can reach 20% to 30%. They are mainly used to configure high-tenacity and high-fluidity concrete or when the water demand needs to be drastically reduced. of concrete. High-efficiency water-reducing admixtures play a significant role in improving the use rate of concrete and can save about 20% of concrete dosage. When ordinary water-reducing agents are used in the granite and artificial stone concrete of the Three Gorges Project, the water demand can reach up to 110 kg/m3. The selected ZB-1A high-efficiency water-reducing agent is used together with DH9 air-entraining agent and Class I fly ash. After joint blending, the water demand dropped to about 85 kg/m3, exceeding the advanced standards of other countries in the world. The Three Gorges Project also uses acrylic acid-based high-efficiency water-reducing agent X404 with a higher water-reducing rate. The water-reducing rate is about 30%. However, this water-reducing agent is relatively expensive and is mainly used in high-toughness concrete locations.
Retarder
Retarder can slow down the initial setting and hardening of concrete. time, which is beneficial to decoration projects; it can slow down the hydration rate of concrete slurry, increase the hydration heat absorption process, and is beneficial to the temperature control of large-volume concrete. The retarder will further reduce the initial strength of the concrete in 1 to 3 days, but it will not affect the normal transformation of the final strength.
Usually retarders can increase the initial setting time of concrete by 1 to 4 hours, but this is insufficient for concrete pouring in large warehouses under high temperature conditions. . In order to meet the needs of large-volume concrete decoration projects in high-temperature areas and high-temperature seasons, the national "Eighth Five-Year Plan" scientific and technological research project has developed high-temperature retarder. This type of retarder can be used when the weather is (35+2) ℃ and the air humidity is (60+5) % standard, the initial setting time of concrete is 6 to 8 hours. Currently, many retarding high-efficiency superplasticizers used in construction projects such as Xilingxia will make the initial setting time of concrete exceed 6 to 8 hours if the dosage is increased appropriately. Taking into account the large warehouse surface in high temperatures around 35°C Concrete pouring is required.
Air-entraining agent
Air-entraining agent is a zwitterionic organic substance, which is a concrete The most common water-reducing agent, it can make the concrete introduce many small, uniform and open bubbles from the air during the mixing process, so that the concrete contains a sufficient amount of air. A good air-entraining agent can introduce as many as 1 billion bubbles into the concrete, with diameters ranging from 0.05 to 0.2 mm. They are usually discontinuous open spherical shapes with even distribution and good reliability, which can significantly improve the quality of the concrete. The cold resistance and performance of the soil (the internal concrete of the Three Gorges Project can withstand freeze-thaw cycles up to about 150 times, and the external concrete up to about 300 times); at the same time, it can also improve the workability of the concrete, especially artificial stone or volcanic rock sand. The particles are coarser, the mix ratio is weak, and its application in cement-poor concrete is stronger; it improves the bleeding and segregation of concrete; it reduces the hydrophilicity of concrete and improves the corrosion resistance potential of concrete.
The dosage of air-entraining agent is usually in the range of 0.3 to 20,000 of the net weight of concrete. Because the dosage is small, it must be weighed accurately and stirred evenly. . In addition, there are many factors that affect air entrainment consumption, such as water-cement ratio, concrete dosage, sand rate, aggregates, vibration methods, mixing time, collapse degree, forming temperature, etc., all of which need to be used in strict standards, otherwise the standards will not be reached. It needs to be effective.
Coated superplasticizer
Coated superplasticizer has two main functions: Functional water reducing agents, such as retarding water reducing agents, have both retarding and water reducing effects, and air entraining water reducing agents have both air entraining and water reducing effects.
Many hydropower installation projects, especially the Three Gorges Project, use two types of water reducing agents, such as retarding high-efficiency water reducing agents and air entraining agent coatings , it also has the functions of efficient water reduction, air entrainment and retardation, and has achieved very good results. It not only meets the requirements of retarding concrete for large warehouse surfaces, but also achieves the purpose of reducing water and improving performance.
Standards for the use of water-reducing agents
What water-reducing agents should be used in a construction project Careful selection should be carried out before the construction of the project in accordance with architectural design and decoration technical standards, and strict adaptability tests and explanations should be carried out based on the raw materials. In the early stages of construction of the Three Gorges Project, nearly 30 reliable water-reducing agent manufacturers from various provinces were inspected.More than 30 types of products produced by the company have undergone preliminary trials in accordance with national industry standards. On this basis, several high-quality products that have been initially reviewed have been carried out by three qualified experimental companies with raw materials from the Three Gorges Project. A comprehensive experiment on the adaptability of concrete, after sufficient discussion and rigorous review, finally selected 2 to 3 quality-selected water-reducing agent types that are suitable for the actual conditions of the Three Gorges Project, taking into account large warehouse areas and high-toughness concrete pouring. It is necessary to improve various properties of concrete and obtain good economic benefits.
In order to facilitate management, it is appropriate to select 1 to 2 similar water reducing agents (including reserved others) for a large, medium and small construction project. Under normal circumstances , there is no need to change the type of water reducing agent at will during construction.
Depending on other materials, although the dosage of water-reducing agent is too small, it is very important to the quality of concrete, so its dosage has been verified through experiments After it is clarified, it should be strictly controlled. The quality and reliability of the water-reducing agent should be strictly tested in the original factory and during the use process in accordance with relevant standards. The transportation and storage of water-reducing agents should also be strictly observed in accordance with relevant national standards.
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